DESCRIPTION: Agricultural workers are exposed to high concentrations of airborne microorganisms, and thus have an increased risk for developing respiratory diseases. Respirators, when properly selected and used, can decrease the exposures in agricultural environments. In this study, a new field-compatible method will be developed to dynamically measure the protection provided by respirators against dust in agricultural environments. Another method will be developed to determine the protection provided by respirators against fungal and actinomycete spores. The new methods will be evaluated first in the laboratory under controlled conditions using four test aerosols: NaCl, PSL and fungal and actinomycete spores. The laboratory tests will be conducted using three different respiratory flow rates, three different concentrations for test particles and three different sampling probe locations. After that, the new methods will be tested in the field during different agricultural operations while farmers are using the new N95 filtering facepiece respirators. The field evaluation will be performed during different tasks: feeding animals, seeding, harvesting. Tests related to animal feeding will be performed during two seasons, in the fall and in the winter, when the concentrations in the animal confinements are expected to be most significantly different. The field testing will include both small-scale and large-scale farming operations. The design of the proposed laboratory and field experiments will include a combination of traditional time-consuming microbiological methods and of advanced dynamic and compact aerosol measurement techniques. This dual approach combined with our extensive experience on respirator and bioaerosol studies will allow us to collect a representative data bank in the shortest possible time. The results will include dynamic measurements of respiratory protection as a function of time and particle size. The field testing will be conducted for different agricultural activities in different seasons. The data will provide the basis for recommendations and, if desired, regulations for the respiratory protection of agricultural workers against organic dust. The methods developed and tested in this study are critically needed for further epidemiological and intervention studies in agricultural and other occupational environments.